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Optimer will host an investor and analyst reception on
October 8, 2012 at
9:00 a.m. Eastern time in
New York City to expand on the strategy described above, provide a long-term outlook for DIFICID market penetration, and review third quarter 2012 top-line revenues. A live audio webcast of the event will be accessible on the Investors page of the Company's website at
www.optimerpharma.com and may also be accessed via listen-only dial in at (877) 442-2965 for U.S. callers and +1- (760) 298-5087 for international dialers. The access code for the call is 37429762. Presentation replays will be available at the same location for 90 days following the presentation.

About Clostridium difficile-associated Diarrhea (CDAD)

Clostridium difficile infection (CDI) is a serious illness resulting from infection of the inner lining of the colon by
C. difficile bacteria, which produce toxins that cause inflammation of the colon, severe diarrhea and, in the most serious cases, death.
Clostridium difficile-associated diarrhea is the most common symptom of CDI. In recent years,
C. difficile has surpassed methicillin-resistant
Staphylococcus aureus (MRSA) as the leading cause of healthcare-acquired infections in community hospitals. Patients typically develop CDAD from the use of broad-spectrum antibiotics that disrupt normal gastrointestinal (gut) flora, possibly allowing
C. difficile bacteria to flourish.

About DIFICID® (fidaxomicin) Tablets

DIFICID is the first macrolide antibacterial drug indicated for
Clostridium difficile-associated diarrhea (CDAD) to be approved in over 25 years in the U.S. It is indicated for the treatment of CDAD in adults 18 years of age or older. DIFICID is administered in 200 mg tablets given orally twice daily.

Important Safety Information for DIFICID

DIFICID should not be used for systemic infections. Only use DIFICID for infection proven or strongly suspected to be caused by
C. difficile. Prescribing DIFICID in the absence of a proven or strongly suspected
C. difficile infection is unlikely to provide benefit to the patient and increases the risk of the development of drug resistant bacteria. The most common adverse reactions are nausea (11%), vomiting (7%), abdominal pain (6%), gastrointestinal hemorrhage (4%), anemia (2%) and neutropenia (2%).

Please visit www.DIFICID.com or call 855-DIFICID (343-4243) for full prescribing information for DIFICID.